Recent progress in meta-optics, particularly the development of metasurfaces, has enabled compact, tunable, and integrable control over the amplitude, phase, polarization, and wavefront of light, thereby allowing a paradigm shift in traditional optical science and engineering. In parallel, the ability to generate and precisely manipulate nonclassical light is central to quantum optics, enabling key functionalities in secure quantum communication, precision measurement, and scalable quantum computation. This review aims to bridge these two rapidly advancing fields by presenting recent progress in the application of structured materials to the manipulation of quantum states of light. We begin by introducing the concept of singular optics, followed by a discussion of various families of spatially and temporally structured beams that form the foundation for many of the phenomena explored in quantum photonics. Next, we revisit the theoretical framework of quantum optics, including the formalism of photon quantization and the principles governing quantum frequency conversion. We then examine how metasurfaces can be engineered to enable highly efficient nonlinear quantum processes, including both up-conversion and down-conversion, thereby offering new approaches for generating and controlling complex quantum states. Furthermore, we discuss the crucial role of structured materials in shaping the properties of quantum light and in applications such as quantum ghost imaging. The review concludes by identifying emerging directions for integrating meta-optical platforms with quantum systems, highlighting their potential for scalable manipulation of nonclassical light at the nanoscale.
Recent progress in meta-optics, particularly the development of metasurfaces, has enabled compact, tunable, and integrable control over the amplitude, phase, polarization, and wavefront of light, thereby allowing a paradigm shift in traditional optical science and engineering. In parallel, the ability to generate and precisely manipulate nonclassical light is central to quantum optics, enabling key functionalities in secure quantum communication, precision measurement, and scalable quantum computation. This review aims to bridge these two rapidly advancing fields by presenting recent progress in the application of structured materials to the manipulation of quantum states of light. We begin by introducing the concept of singular optics, followed by a discussion of various families of spatially and temporally structured beams that form the foundation for many of the phenomena explored in quantum photonics. Next, we revisit the theoretical framework of quantum optics, including the formalism of photon quantization and the principles governing quantum frequency conversion. We then examine how metasurfaces can be engineered to enable highly efficient nonlinear quantum processes, including both up-conversion and down-conversion, thereby offering new approaches for generating and controlling complex quantum states. Furthermore, we discuss the crucial role of structured materials in shaping the properties of quantum light and in applications such as quantum ghost imaging. The review concludes by identifying emerging directions for integrating meta-optical platforms with quantum systems, highlighting their potential for scalable manipulation of nonclassical light at the nanoscale.
The convergence of metamaterials and quantum optics heralds a transformative era in photonic technologies, poised to revolutionize applications ranging from information processing and imaging to sensing and beyond. This review explores the synergistic integration of metasurfaces—engineered sub-wavelength planar structures—and quantum optics, which exploits quantum mechanical principles to manipulate light at the most granular level. We outline the design principles, fabrication processes, and computational challenges involved in creating quantum metasurfaces, discussing both forward and inverse design approaches. Advances in nanofabrication and intelligent optimization techniques, such as machine learning and topology optimization, have enabled the development of metasurfaces with unparalleled control over electromagnetic waves. We examine recent progress in using quantum metasurfaces for single-photon and multi-photon generation, quantum imaging, and quantum sensing, showcasing how these innovations achieve unprecedented precision and novel functionalities. Additionally, we highlight the integration of metasurfaces into quantum light manipulation, emphasizing their role in enhancing wavefront shaping and entanglement control. By providing a comprehensive survey of current advancements and future research directions, this review highlights the vast potential of metasurfaces and quantum optics at the crossroads, setting the stage for next-generation technological innovations that will define the forthcoming decade.
Optical metasurfaces, i.e., subwavelength planar nanostructures, have attracted increasing attention due to their unprecedented capabilities of molding classical light and revolutionized conventional optics by replacing bulky optical components with ultrathin, lightweight, and ultracompact meta-optics. In addition to controlling classical light, meta-optics demonstrate the potential to efficiently manipulate nonclassical light and start to enter the realm of quantum photonics. Here, we briefly overview recent advances in quantum meta-optics for generation and manipulation of nonclassical light, highlighting innovative approaches, and discuss future opportunities in this burgeoning area, ranging from fundamental research to practical applications.
Quantum light sources are essential building blocks for many quantum technologies, enabling secure communication, powerful computing, and precise sensing and imaging. Recent advancements have witnessed a significant shift toward the utilization of "flat" optics with thickness at subwavelength scales for the development of quantum light sources. This approach offers notable advantages over conventional bulky counterparts, including compactness, scalability, and improved efficiency, along with added functionalities. This review focuses on the recent advances in leveraging flat optics to generate quantum light sources. Specifically, the generation of entangled photon pairs through spontaneous parametric down-conversion in nonlinear metasurfaces, and single photon emission from quantum emitters including quantum dots and color centers in 3D and 2D materials are explored. The review covers theoretical principles, fabrication techniques, and properties of these sources, with particular emphasis on the enhanced generation and engineering of quantum light sources using optical resonances supported by nanostructures. The diverse application range of these sources is discussed and the current challenges and perspectives in the field are highlighted.
Quantum imaging leverages entanglement and photon correlations to surpass classical limits in resolution and noise performance. However, its practical deployment is constrained by bulky optical setups and limited system adaptability. Metasurfaces—ultrathin, subwavelength-structured devices—offer a compact and reconfigurable solution for wavefront control in quantum light fields. This review presents recent advances in geometric-, propagation-, and hybrid-phase metasurface designs, showcasing their contributions to enhanced spatial resolution, improved visibility, and system miniaturization across applications such as ghost imaging, quantum holography, and single-photon microscopy. It also examines key challenges—including photon loss, fabrication-induced phase noise, and the lack of dynamic tunability—while outlining future directions for developing integrated, noise-resilient, and task-specific quantum imaging platforms.
The recent advent of optical metasurfaces, ultra-thin structures composed of nanoresonators facilitating strong light concentration [1–3], opens the path towards efficient \nfrequency conversion [4–7] in a material thousand times thinner than a human hair [8]. \nThere is a remarkable capacity to individually shape each nanoresonator of the metasurface to spatially and spectrally control the conversion process with unprecedented \nnanoscale resolution, facilitating an ultimate flexibility to selectively convert, focus, \nand image different colours with a single metasurface. The strong enhancement of the \nnonlinear processes in dielectric nanoresonators is largely due to the absence of material \nabsorption and the excitation of Mie-type bulk resonances [2]. The highest conversion \nefficiency to date has been achieved employing III-V semiconductor nanostructures, \nsuch as AlGaAs which is a non-centrosymmetric material with high quadratic nonlinear \nsusceptibility. In particular, second-harmonic generation efficiencies up to 10−4 have \nbeen recently demonstrated [8–12], six orders of magnitude higher than in plasmonics. \nSuch capabilities can make an immense fundamental and practical impact, including \nthe quantum state generation in nonlinear metasurfaces as we discuss in this chapter. \nThe quantum state of correlated photon-pairs is the essential building block for photon entanglement [13, 14], which underpins many quantum applications, including secure networks, enhanced measurement and lithography, and quantum information processing [15]. One of the most versatile techniques for the generation of correlated photons is the process of spontaneous parametric down-conversion (SPDC) [16, 17], see \nFig. 1. It allows for an arbitrary choice of energy and momentum correlations between \nthe generated photons, robust operation at room temperature, as well as for spatial and \ntemporal coherence between simultaneously pumped multiple SPDC sources. Alternative approaches based on atom-like single photon emitters, such as solid-state fluorescent atomic defects [18], quantum dots [19, 20], and 2D host materials [21, 22], have \nreached a high degree of frequency indistinguishability, purity and brightness [19, 20]. \nHowever, this comes with the expense of operation at cryogenic temperatures and lack \nof spatial coherence between multiple quantum emitters. These features might limit \npossible applications and reduce the potential for device scalability. Furthermore, the \nsmall size of the atomic sources often requires complex schemes aimed at coupling to \noptical nanoantennas and improving the photon extraction efficiency [21]. \nThe miniaturization of SPDC quantum-light sources to micro and nanoscale dimensions is a continuing quest, as it enables denser integration of functional quantum \ndevices. Traditionally, bulky cm-sized crystals were utilized for SPDC, entailing the \ndifficulty of aligning multiple optical elements after the SPDC crystal, while offering \nrelatively low photon-pair rates [17]. As a first step of miniaturization, SPDC was \nrealized in low-index-contrast waveguides, which allowed confining light down to several square micrometers transversely to the propagation direction, significantly enhancing the conversion efficiency [23]. However, this approach still requires centimetres \nof propagation length, which makes the on-chip integration with other elements challenging [24]. The introduction of high-index contrast waveguides and ring resonators \nallowed for shrinking the sizes necessary for SPDC to millimetres [25], and to tens \nof micrometers [26]. However, further miniaturisation down to the metasurfaces composed of nanoresonators requires conceptually different approaches.
In recent decades, quantum information technologies have attracted significant attention and experienced rapid development due to their ultrafast processing speeds and high level of information security. A significant trend in this field of study involves the ongoing pursuit of integrating and miniaturizing quantum devices. Metasurfaces, which are artificially designed planar nanostructure arrays with versatile wavefront shaping capabilities, present a promising platform for the development of integrated photonic quantum devices by effectively controlling quantum light in multiple degrees of freedom. In this review, recent advances in the field of quantum photonics facilitated by metasurfaces, encompassing quantum light sources, manipulation and measurement of quantum states, and the intriguing functionalities of quantum metasurfaces, are summarized. Additionally, potential future directions for the advancement of quantum metasurfaces are discussed.